Physics 201 MWF10:20 Fall 2002 (Ford)

Final Exam Chapts. 1--17 in Cutnell and Johnson 5th ed

Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.

(9 pts) 1. A uniform disk is free to rotate about a vertical axis through its center. The disk has radius R = 0.5 m and a moment of inertia about the axis of 240 kg·m². The disk is initially at rest. At t = 0 a constant tangential force of 20 N is applied to the rim of the disk. What is the kinetic energy of the disk at t = 5.0 s?




Ans. ___5.21 J____


(7 pts) 2. Two loud speakers A and B are driven by the same amplifier and therefore emit sound waves in phase and with the same frequency f. Speaker B is 10.0 m to the right of speaker A. Point P is 2.0 m to the right of speaker A and therefore 8.0 m to the left of speaker B. The speed of sound in air is 343 m/s. What is the smallest nonzero frequency f for which destructive interference will occur at point P?




Ans. ____28.6 Hz___


(8 pts) 3. A student is measuring standing wave frequencies for a string 1.2 m long that is tied down at both ends. The wave speed is kept constant while the frequency of the waves is varied. The student finds two successive standing wave frequencies to be 150 Hz and 180 Hz. The 150 Hz standing wave is not the lowest frequency standing wave.

a) What is the fundamental frequency?

Ans.____30 Hz___

b) For the 150 Hz standing wave, what is the distance between adjacent nodes?

Ans. ____0.24 m___


(12 pts) 4.

a) 3.0 moles of a monatomic ideal gas expands adiabatically and in the process does 610 J of work. What is the change in the temperature of the gas? Does the temperature of the gas increase or decrease?

Ans. ___-16.3 K___

increase or decrease? ___decreases___

b) 3.0 moles of a monatomic ideal gas at a temperature of 300K undergoes an isothermal process during which 300 J of heat energy flows into the gas. What is the work W for this process? Does the volume of the gas increase or decrease?

Ans.___300 J___

increase or decrease? ___increases___

c) In a constant volume process for 3.0 moles of a monatomic ideal gas, the internal energy of the gas increases from 200 J to 500 J. What is the heat flow Q for this process? Does heat energy flow into the gas or out of the gas?

Ans. ___+300 J___

increase or decrease? ___into___


(12 pts) 5. A 5 kg block starts from rest at point A the bottom of an incline that slopes upward at an angle of 37° above the horizontal. A constant force P = 50 N that is parallel to the surface of the incline is applied to the block and the block travels 12 m up the incline to point B. The block has 160 J of kinetic energy when it reaches point B.




a) How much work is done on the block by the force P during the block's displacement from A to B?

Ans. ___+600 J___

b) How much work was done on the block by the normal force on the block during the block's displacement from A to B?

Ans. ____0___

c) How much work was done on the block by the gravity force on the block during the block's displacement from A to B?

Ans. ____-354 J____

d) How much work was done on the block by the friction force on the block during then block's displacement from A to B?

Ans. ____-86 J____


(12 pts) 6. A block of mass 10 kg sits on a ramp inclined at 37° above the horizontal. A light rope that passes over a light, frictionless pulley connects the 10 kg block to a block of mass m that hangs from the other end of the rope. The blocks are released from rest and it is observed that the hanging block moves downward with an acceleration of 2.0 m/s². While the blocks are moving, the tension in the rope is 95 N.




a) What is the mass m of the hanging block?

Ans. ____12.2 kg___

b) Calculate the normal force that the ramp exerts on the 10 kg block.

Ans. ____78.3N____

c) What is the coefficient of kinetic friction between the 10 kg block and the ramp?

Ans. ____0.204____


(12 pts) 7. A rock is thrown from the roof of a building with a velocity of 20 m/s at 53° above the horizontal. The rock is observed to strike the ground a horizontal distance of 96 m from the base of the building. Neglect air resistance.




a) How long after it was thrown does the rock strike the ground?

Ans. ___5 s___

b) What is the height of the building?

Ans. ____42.5 m____

c) What is the speed of the rock just before it strikes the ground?

Ans. ___35.1 m/s_____


(10pts) 8. A 5 kg rock is tied to one end of a string. The other end of the string is tied to the top of a vertical rod. The rock is set into motion so that it moves in a horizontal circle and the string makes a constant angle of 37° with the rod.




a) What is the tension in the string?

Ans. ____61.4 N___

b) What is the magnitude of the acceleration of the rock?

Ans. ____7.39 m/s²_____

c) How long does it take the rock to make one revolution?

Ans. ____2.53 s____


(8 pts) 9. A bullet with mass 0.02 kg is fired eastward with speed v₀ towards a rock of mass $m$ that is at rest on a horizontal, frictionless surface. The bullet strikes the rock and moves off at 30 m/s due south. As a result of being hit by the bullet, the rock moves at 4 m/s in the direction 37° north of east. Neglect gravity.




a) What is the mass m of the rock?

Ans. _____0.25 kg____

b) What is the initial speed v₀ of the bullet?

Ans. ____40 m/s____


(10 pts) 10. A uniform bar 6 m long weighing 30 N is attached by a frictionless hinge to the wall. A block weighing 40 N is suspended from the bar, 4 m from the hinge. The bar is held in the horizontal position by a light rope that runs between the wall and the end of the bar. The rope makes an angle of $37^\circ$ with the bar.




a) What is the tension in the rope?

Ans. ____69.4 N__

b) What is the vertical component of the force the hinge exerts on the bar? Is this component upward or downward?

Ans. _____28.2 N____

_____upward_________